This paper analyses the results of two series of experiments concerned with the response
of a single vertical cylinder in the inertia regime in steep non-breaking waves. We recorded
first the loading on a cylinder when it was held stationary, and secondly, its response in
the same waves when it was pivoted just above the floor of the wave flume, and supported at
the top by springs in the horizontal plane. Spring stiffnesses were set to achieve natural
frequencies (measured in still water) in the range between 3 and 11 times the dominant wave
frequency. The experiments were repeated with cylinders of three different diameters.
Peak loading on stationary cylinders was found to exceed the predictions of a Morison
model (based on kinematics computed from a numerical model of the measured waves), though
improvements were achieved through the inclusion of slender-body terms. Measured ringing
responses are generally in good agreement with those computed on a quasi-static basis from
the measured loading history, but in some conditions, particularly at low frequency ratios,
there is clearly some feedback from the motion to the excitation. Peak accelerations in the
steepest waves are found to be limited approximately to those that would occur if the
maximum loading were applied as a step change. Particular attention is given to a rapid
cycle of loading that occurs after the crest has passed the cylinder's axis, and to images
of the flow around the cylinder at the water surface.